A hybrid vehicle is a next generation vehicle which reduces exhaust gas emissions and provides efficient gas mileage by employing motor power as well as internal combustion engine power.
Generally, as shown in FIG. 4, in the hybrid vehicle, an engine 10, a motor 20, and an automatic transmission 30 are arranged in series. The engine 10 and the motor 20 are connected to each other to transfer power via an engine clutch 40.
The hybrid vehicle can drive in two different modes which may be classified as an electric vehicle (EV) mode using only a motor power of the motor 20, and a hybrid electric vehicle (HEV) mode using torque of the engine 10 as a main power and torque of the motor 20 as an auxiliary power.
The engine clutch actuator of a dual clutch transmission (DCT) employed in the hybrid vehicle transfers hydraulic pressure required for coupling or releasing the engine clutch by converting the torque generated from the motor into rectilinear movement.
When the hybrid vehicle is driven in the EV mode and while the actuator operates according to a characteristic of a normally closed type clutch, the clutch is released so that the motor can be used as the main power source.
However, the engine clutch actuator installed in the hybrid vehicle according to the related art can only sense pressure of a cylinder and a reservoir by using a pressure sensor, and supplements brake oil by driving a piston without having any additional fail-safe strategy.
Therefore, in the hybrid vehicle according to the related art, when the engine clutch actuator fails to operate, the rectilinear movement of the piston ceases, thus making it difficult to switch from the EV mode to the HEV mode in the hybrid vehicle. In addition, when the engine clutch actuator does not operate during the EV mode, power consumption increases to maintain the EV mode since the EV mode is forced to operate, thereby deteriorating the fuel efficiency.